In the combustion of a fuel, such as coal, oil, peat, waste, etc., in a combustion plant, such as a power plant, a hot process gas is generated, such process gas containing, among other components, carbon dioxide CO2. With increasing environmental demands various processes have been developed for removing carbon dioxide from the process gas. One such process is the so called oxy-fuel process, an example of which is disclosed in US 2007/0243119. In an oxy-fuel process a fuel, such as one of the fuels mentioned above, is combusted in the presence of a nitrogen-lean gas. Oxygen gas, which is provided by an oxygen source, is supplied to a boiler in which the oxygen gas oxidizes the fuel. In the oxy-fuel combustion process a carbon dioxide rich flue gas is produced, the carbon dioxide content of which can be compressed in a separate unit and be disposed of in order to reduce the emission of carbon dioxide into the atmosphere.
The carbon dioxide, CO2, generated in an oxy-fuel process is normally compressed to a high pressure, or even liquefied, prior to being disposed of. The compression of the carbon dioxide is associated with stringent requirements for low concentrations of impurities. One such impurity is sulphur dioxide, which is generated when sulphur containing compounds of the fuel are oxidized during the combustion process. WO 2009/052775 discloses a wet scrubber that may be utilized for removing sulphur dioxide from a process gas generated in an oxy-fuel combustion process. The wet scrubber of WO 2009/052775 may in some situations not be efficient enough with respect to the required sulphur dioxide removal efficiency.